Dual Ignition
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Dual Ignition is a system for spark-ignition engines, whereby critical ignition components, such as
spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...
s and
magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...
s, are duplicated. Dual ignition is most commonly employed on aero engines,Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 177. Aviation Supplies & Academics, 1997. Aviation Publishers Co. Limited, ''From the Ground Up'', (27th revised edition), page 67, and is sometimes found on cars and motorcycles. Dual ignition provides two advantages: redundancy in the event of in-flight failure of one ignition system; and more efficient burning of the fuel-air mixture within the combustion chamber. In aircraft and gasoline-powered fire fighting equipment, redundancy is the prime consideration, but in other vehicles the main targets are efficient combustion and meeting emission law requirements.


Efficiency

A dual ignition system will typically provide that each cylinder has twin
spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...
s, and that the engine will have at least two ignition circuits, such as duplicate
magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...
s or
ignition coil An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. So ...
s. Dual ignition promotes engine efficiency by initiating twin flame fronts, giving faster and more complete burning and thereby increasing power. Although a dual ignition system is a method of achieving optimum combustion and better fuel consumption, it remains rare in cars and motorcycles because of difficulties in siting the second plug within the cylinder head (thus, many dual ignition systems found on production automobiles typically were of a two valve design rather than a four valve). The
Nash Ambassador The Nash Ambassador is a luxury automobile that was produced by Nash Motors from 1927 until 1957. For the first five years it was a top trim level, then from 1932 on a standalone model. Ambassadors were lavishly equipped and beautifully construc ...
for 1932-1948 used twin sparkplugs on the straight eight engine, while later Alfa Romeo Twin Spark cars use dual ignition, as do Honda cars with the i-DSI series engines, and Chrysler's Modern Hemi engine. In 1980 Nissan installed twin sparkplugs on the Nissan NAPS-Z engine, with
Ford Ford commonly refers to: * Ford Motor Company, an automobile manufacturer founded by Henry Ford * Ford (crossing), a shallow crossing on a river Ford may also refer to: Ford Motor Company * Henry Ford, founder of the Ford Motor Company * Ford F ...
introducing it on the 1989
Ford Ranger Ford Ranger is a nameplate that has been used on multiple model lines of pickup trucks sold by Ford worldwide. The nameplate has been used for distinct model lines of vehicles worldwide since 1982 from the compact and mid-size pickup category. ...
and 1991
Ford Mustang The Ford Mustang is a series of American automobiles manufactured by Ford. In continuous production since 1964, the Mustang is currently the longest-produced Ford car nameplate. Currently in its sixth generation, it is the fifth-best selli ...
four-cylinder models. Several modern Mercedes-Benz engines also have two spark plugs per cylinder, such as the M112 and M113 engines. Some motorcycles, such as the Honda VT500 and the Ducati Multistrada, also have dual ignition. The 2012 Ducati Multistrada was upgraded with "twin-plug cylinder heads for smoother, more efficient combustion", the change contributing to a 5% increase in torque and a 10% improvement in fuel consumption. Early
BMW R1100S The BMW R1100S is a sports motorcycle that was manufactured by BMW Motorrad between 1998 and 2005. Introduced some 25 years after the R90S, the company's first sports bike, the R1100S was the first BMW bike having clip-on handlebars, rearset foot ...
bikes had a single spark plug per cylinder, but after 2003 they were upgraded to dual ignition to meet emission law requirements.


Safety

Dual ignition in aero-engines should enable the aircraft to continue to fly safely after an ignition system failure. Operation of aero engines on one magneto (rather than both) typically results in an rpm drop of around 75 rpm. Its existence on aviation powerplants dates back to the
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
years, when such engines as the
Hispano-Suiza 8 The Hispano-Suiza 8 was a water-cooled V8 SOHC aero engine introduced by Hispano-Suiza in 1914, and was the most commonly used liquid-cooled engine in the aircraft of the Entente Powers during the First World War. The original Hispano-Suiza ...
and Mercedes D.III, and even
rotary engine The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and i ...
s as the later
Gnome Monosoupape The ''Monosoupape'' ( French for single-valve), was a rotary engine design first introduced in 1913 by Gnome Engine Company (renamed Gnome et Rhône in 1915). It used a clever arrangement of internal transfer ports and a single pushrod-operated ...
model 9N versions featured twin spark plugs per cylinder. The
Hewland AE75 Hewland is a British engineering company, founded in 1957 by Mike Hewland, which specialises in racing-car gearboxes. Hewland currently employ 130 people at their Maidenhead facility and have diversified into a variety of markets being particul ...
, an inline three cylinder aero-engine created for the
ARV Super2 The ARV Super2 (''Air Recreational Vehicle'') is a British two-seat light aircraft with strut-braced shoulder wings and tricycle landing gear. Designed by Bruce Giddings, the Super2 was available either factory-built or as a kit. It was in ...
, had three ignition circuits, each circuit serving a plug in two different cylinders. If just one of the three circuits failed, all three cylinders still received sparks, and even if two circuits were to fail, the remaining circuit would keep the engine running on two cylinders.


Partial dual ignition

While true dual ignition uses completely separate and redundant systems, some
certified Certification is the provision by an independent body of written assurance (a certificate) that the product, service or system in question meets specific requirements. It is the formal attestation or confirmation of certain characteristics of a ...
engines, such as the Lycoming O-320-H2AD use a single engine magneto drive-shaft turning two separate magnetos. Whilst saving weight, this creates a
single point of failure A single point of failure (SPOF) is a part of a system that, if it fails, will stop the entire system from working. SPOFs are undesirable in any system with a goal of high availability or reliability, be it a business practice, software appl ...
in mechanical terms, that could cause both ignition systems to cease working. A simple form of partial dual ignition on some
amateur-built aircraft Homebuilt aircraft, also known as amateur-built aircraft or kit planes, are constructed by persons for whom this is not a professional activity. These aircraft may be constructed from "scratch", from plans, or from assembly kits.Armstrong, Kenn ...
uses a single spark plug, but duplicates the coil and pick-up for better redundancy than traditional single ignition. A further form of partial dual ignition (such as on the Honda VT500) is for each cylinder to have a single HT coil which sends the current to one plug and completes the circuit via the second plug, rather than via the earth. This system requires a voltage sufficient to jump both plug gaps, but an advantage is that if one plug fouls, the fouled plug may burn itself clean while the engine continues running.


Wankel engines

Wankel engine The Wankel engine (, ) is a type of internal combustion engine using an Eccentric (mechanism), eccentric rotary combustion engine, rotary design to convert pressure into rotating motion. It was invented by German engineer Felix Wankel, and desi ...
s have such an elongated combustion chamber that even non-aero wankel engines may adopt dual ignition to promote better combustion. The
MidWest AE series The MidWest AE series are lightweight, liquid-cooled, single- and twin-rotor Wankel engines, with dual ignition, designed for light aircraft. They were produced by Mid-West Engines Ltd. at Staverton Airport, Gloucestershire, UK. History This en ...
Wankel aero-engine has twin plugs per chamber, but these are placed side-by-side, not sequentially, so their main purpose is to give redundancy rather than improved combustion.


Distillate fuel

Richard W. Dilworth of the Electo-Motive Corporation devised a system, using four spark plugs and one carburettor per cylinder, in order to burn "distillate" fuel in train car engines. Because such heavy, but cheap, fuel was hard to ignite, a quadruple system of ignition was used in order to burn fuel roughly equivalent to kerosene or home heating fuel. By using this distillate fuel, that cost as little as one-fifth the price of gasoline before the
Great Depression The Great Depression (19291939) was an economic shock that impacted most countries across the world. It was a period of economic depression that became evident after a major fall in stock prices in the United States. The economic contagio ...
, a railroad could save substantially on fuel costs. However, this patented ignition system saw little commercial use.


References

{{Aircraft piston engine components Engine technology Ignition systems Gasoline engines